Diagnosis
The 'Check Filter' alert is a timer-based reminder you can configure. It is not sensing a dirty filter. The timer has simply reached its set interval.
How to Fix It
To clear the alert, use the physical controller. Press the 'Menu' button. Navigate using the up/down arrows to the 'Filter Reset' option (icon of a fan with a leaf). Press the 'Menu' button to select it. Press the up arrow to confirm 'Reset'. The alert will disappear from the screen.
If That Didn't Work
If the alert returns immediately or the menu option is unresponsive, reset the filter timer via the app. Open the Cielo Home app, select your device, go to Settings > Filter Alert. Tap 'Reset Filter Timer'. You can also disable the alert entirely here by toggling it off.
Heads Up
The default filter alert interval is 90 days. You can customize this in the app from 30 to 180 days. This setting is independent of your actual AC maintenance schedule.